The role of geomorphology in evaluating remediation options for floodplain wetlands: the case of Ramsar-listed Seekoeivlei,eastern South Africa

The range of benefits bestowed by wetlands is today increasingly recognized, and remediation of degraded wetlands is being carried out around the world. Many degraded wetlands are associated with river floodplains, and an essential requirement for their remediation planning is a comprehensive knowledge of the geomorphological functioning of the river channel and floodplain. Here, we review previous geomorphological investigations of the Ramsar-listed Seekoeivlei floodplain wetlands, Free State Province, South Africa, and demonstrate how the knowledge gained is playing a key role in evaluating remediation options that are needed following more than a century of direct and indirect human impacts. Faunal and floral changes, coupled with channel modifications, have altered the flow and sediment regime and initiated major changes to erosional and depositional patterns, including promoting rapid headward growth of a new channel and abandonment of a former channel. These changes have led to further management interventions, including installation of weirs and erosion control structures. In an ideal world, remediation would strive to return a wetland to its natural, pre-impact state but, in reality, other management goals have to be taken into consideration. In the case of Seekoeivlei, these include maintaining current habitat and biodiversity (this has the added advantage of promoting local tourism, especially bird watching), and using the wetlands for water quality enhancement. Attempts to return the wetlands to their pre-impact state (e.g. by removing exotic trees and erosion control structures) would in fact further reduce habitat and biodiversity, permanently in the case of some avian species, and for centuries in the case of some aquatic species, because of the very slow natural rates of channel and floodplain change. Alternative options will all require ongoing intervention, albeit of variable intensity, but in effect will mean that the wetland will never return to its pre-impact state. Remediation will thus create an essentially ‘artificial’ wetland complex that restores some of the ecological and hydrological functions but that is likely to remain very far from its natural geomorphic condition.